Conventionally, a scroll compressor has been used as a compressor to compress a refrigerant in a refrigerating cycle, as disclosed, for example, in Japanese Laid-Open Patent Publication No. 5-312156. The scroll compressor includes a compression mechanism with a fixed scroll and an orbiting scroll that have protruding involute wraps engaged with each other in a casing. The fixed scroll is fixed to the casing by, for example, a fixing member (hereinafter, referred to as a housing) and the orbiting scroll is coupled to an eccentric shaft portion of a drive shaft. Further, the scroll compressor is constituted such that the orbiting scroll just revolves orbitally to the fixed scroll without rotating on its own axis, thereby contracting a compression chamber formed between the wraps of both scrolls to compress the refrigerant therein.
In the scroll compressor, for example, an Oldham coupling has been used to enable the above operation of the orbiting scroll. The Oldham coupling is provided with two pair of keys, which project at its obverse and reverse faces so as to cross each other at a right angle in a direction perpendicular to an axis of the drive shaft. Further, two pair of key grooves are formed at the outer face of the housing and the back face of the orbiting scroll so as to correspond to the above keys. Engagement of the keys with the key grooves prevents the orbiting scroll from rotating on its own axis during the rotation of the derive shaft, while continuous changing of the amount of movement in the direction of each key groove enables its orbital revolution around the rotational axis of the drive shaft.
A lateral-direction load and an axial-direction load act on the orbiting scroll as a reaction force of the refrigerant due to compressing of the refrigerant. Also, a rotational torque acts on the orbiting scroll due to the above lateral-direction load. The rotational torque, which includes a moment (herein, referred to as a first rotational torque) produced by a lateral-direction element of the refrigerant's reaction force as its main element, has a function of making the orbiting scroll rotate on its own axis. The first rotational torque increases or decreases cyclically depending on changing of a refrigerant's pressure in the compression chamber during the orbital revolution of the orbiting scroll, and it becomes the greatest when the orbiting scroll reaches to its revolutionary position where the refrigerant's pressure becomes the greatest.
Further, the rotational torque of the orbiting scroll changes its magnitude depending on moments caused by various factors such as a shape of wrap, a position of the center of gravity of the orbiting scroll, a manufacturing error between the rotational center and the wrap center, a changing inertia force by the movement of Oldham coupling, and operating conditions of the compressor (a moment caused by the inertia force of the Oldham coupling is referred to as a second rotational torque in the present description).
Problem to be Solved
In the meantime, in a so-called symmetric-volute structure having the same length of a fixed-side wrap as that of an orbiting-side wrap, the above rotational torque just changes only in its magnitude, having its unchanging acting direction. Meanwhile, in a so-called asymmetric-volute structure having a different length of the fixed-side wrap from that of the orbiting-side wrap, the rotational torque may not only change in its magnitude in a cycle but also reverse its acting direction. The reason for this is considered as follows. That is, a reaction force of the refrigerant's pressure in the first compression chamber formed between the wrap-outer peripheral face of the orbiting scroll and the wrap-inner peripheral face of the fixed scroll, and a reaction force of the refrigerant's pressure in the second compression chamber formed between the wrap-inner peripheral face of the orbiting scroll and the wrap-outer peripheral face of the fixed scroll may be basically balanced all the time during the orbital revolution of the orbiting scroll in the symmetric-volute structure. In the asymmetric-volute structure, however, there may exist an area where the above reaction forces are imbalanced.
Especially, in particular operating conditions such as a high-speed operation, the inertia force of the Oldham coupling becomes great, and thereby the direction of the rotational torque acting on the orbiting scroll tends to reverse. Accordingly, there was a problem that keys of the Oldham coupling shake in clearances in the key grooves of the hosing and the orbiting scroll, thereby producing a vibration and a noise.
The asymmetric-volute structure shows a tendency that the above vibration and noise occur more noticeably than the symmetric-volute structure. However, even the symmetric-volute structure have also a risk that the vibration of key may occur due to the fluctuation of the rotational torque, and therefore a stable operation with less torque vibration should be desirable for the symmetric-volute structure as well.
In the meantime, it may be possible to improve an involute shape of the wrap by design changing to reduce the rotational torque itself, and it is considered that this design changing may lessen the range of fluctuation of the rotational torque and the risk of the key shaking may reduce. In this case, however, there may be some possibility that design conditions, such as dimension or strength of wrap, or necessary compression characteristics, are not satisfied to the contrary. Accordingly, in fact it was very difficult to design simply to suppress only the rotational torque of the orbiting scroll.
The present invention has been devised in view of the above problems, and an object of the present invention is to suppress the noise and vibration caused by the fluctuation of the rotational torque of the orbiting scroll, without any limited designing of the wrap.